There are two types of single facers for manufacturing single-faced corrugated cardboard sheets by bonding a fluted corrugated medium and a back liner together: a pressure roll type and a pressure belt type. The structure of these types of single facers will be described.
FIG. 7 shows a pressure roll type single facer. In FIG. 7, this single facer 100A includes a pair of upper and lower corrugating rolls 102 and 104, a pressure roll 106 provided so as to face the lower corrugating roll 104, and a gluing unit 108.
The upper and lower corrugating rolls 102 and 104 have flute-shaped grooves in the outer periphery surfaces aligned in the axial direction, and the grooves intermesh with each other. A flat sheet corrugated medium “d” is fed from the direction of the arrow “a”, and is passed through the nip between the upper and lower corrugating rolls 102 and 104, thereby being shaped into a fluted corrugated medium “e”. In the gluing unit 108, glue “g” reserved in glue container 110 is skimmed by a gluing roll 112, and a doctor roll 114 screeds the film of the glue. The glue “g” sticking on the surface of the gluing roll 112 is applied on the flute tips of the fluted corrugated medium “e”.
A flat sheet back liner “f” fed to the pressure roll 106 passes the nip between the pressure roll 106 and the lower corrugating roll 104, together with the fluted corrugated medium “e” on which the glue is applied, and is pressed. Thereby, the fluted corrugated medium “e” and the back liner “f” are bonded together, and a single-faced corrugated cardboard sheet “h” is manufactured.
Next, a structure of a pressure belt type single facer is briefly explained with reference to FIG. 8. In place of the pressure roll 106, this single facer 100B is provided with an endless pressure belt 116 which is pressed against the surface of an upper corrugating roll 102. A flat sheet corrugated medium “d” fed to a lower corrugating roll 104 is passed between the upper and lower corrugating rolls 102 and 104, thereby being shaped into a fluted corrugated medium “e”.
Next, glue “g” is applied on the flute tips of the fluted corrugated medium “e” by a gluing roll 112. Thereafter, the flat sheet back liner “f” and the fluted corrugated medium “e” having the glue “g” applied on its flute tips are passed between the upper corrugating roll 102 and the endless pressure belt 116, to press them and bond them together. In this manner, a single-faced corrugated cardboard sheet “h” is manufactured.
Downstream of the production line, a flat sheet front liner is bonded to flute tips of the single-faced corrugated cardboard sheet thus manufactured, to which the back liner “f” is not bonded, to manufacture a double-faced corrugated cardboard sheet. It is noted that a fluted shape defined by the fluted corrugated medium “e” is referred to as a flute.
Upper and lower corrugating rolls of a single facer are manufactured from a high-strength steel, and hard chromium plating, tungsten carbide spraying, or the like, is provided on the surfaces of the corrugating rolls to provide high wear resistance. However, corrugating rolls wear as they are used. When corrugating rolls wear significantly, they are replaced at regular intervals. Then, the outer surfaces of the corrugating rolls are repolished for reusing the rolls. Since the corrugating rolls are wider than paper sheets, the corrugating rolls do not wear evenly in the width direction and the center portions of the corrugating rolls wear faster. Therefore, the corrugating rolls must be repolished such that the fluted surfaces become even in the width direction.
Patent Reference 1 discloses an improved fluted shape for a corrugating roll for preventing damages in the corrugating roll due to wear of the surface of the corrugating roll caused by friction between paper sheets and the corrugating roll.
Patent Reference 2 discloses a method of polishing corrugating rolls, which can feed paper sheets between the corrugating rolls evenly in the width direction, thereby preventing wrinkle of the paper sheets.